arm, imx6, aristainetos: board updates

- use linux display timing settings
- change backlight duty cycle 500ns
- some defaultenvironment changes
- change fit_addr_r to 0x14000000 as needed if
  MAX_LOCKDEP_SUBCLASSES in linux gets increased.
- Environment now at 0xd0000 in nand flash

Signed-off-by: Heiko Schocher <hs@denx.de>